Pyrometer-scale.



G. A. SHOOK. PYROMETER SCALE- APPLICATION FILED act. 2. 191a.

Patented Aug. 29, 1916.

INVENTOR WITNESSES ms mmms PEYERS 50.. Puomurna. WASHING nm. a. c.

GLENN A. SHOCK, 0F UBBANA, ILLINOIS, ASSIGNOIR T0 SCIENTIFIC MATERIALS COM- PANY, 0F PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

PYROMETER-SCALE.

Specification of Letters Patent.

Application filed. October 2, 1913. Serial No. 793,058.

To all whom it may concern:

Be it known that I, GLENN A. Simon, a citizen of the United States, residing at Urbana, in the county of Ghampaign and State of Illinois, have invented certain new and useful Improvements in Pyrometer- Scales, of which the following is a specification.

My invention relates to total radiation pyrometer scales and its object is to provide means for enabling the true temperature of incandescent bodies in the open or under conditions not representing black body to be obtained.

In the accompanying drawings, Figure 1 is a diagrammatic View of a current measuring instrument which is used in connection with a total radiation pyrometer and which is calibrated to indicate the temperatures measured by the total radiation pyrometer; Fig. 2 is a like View of a similar in strument but which is provided with an extension scale which is used when the pyrometer proper is altered to measure high temperatures; and Fig. 3 is illustrative of cer tain principles of the invention.

The total radiation pyrometer referred to herein is oneof ordinary construction and based upon the Steffan-Boltzmann fourth power radiation law, .and the particular construction thereof need not be here described.

Referring to the drawing, 1 is a pointer movable over-a scale 2 located directly under said pointer, and is adapted to indicate the true temperature in degrees .-centigrade, or Fahrenheit, of a hot body under black body conditions, that is, when said hot body is inclosed by heated walls. In practice the pointer is actuated in the usual way by thermoelectric currents. Also, directly under pointer 1, and concentric with scale 2, is a second scale 3 adapted to indicate the true temperature of a hot body when the latter is not under black body conditions. 4: designates a plane mirror which is sometimes used to facilitate correct reading of the position of the pointer.

As shown in Fig. 2, scale 6 and scale 8, which latter is merely an extension of 6, are adapted to indicate the true temperature of a bodyunder black body conditions, while scale 7 and scale 9, which is an extension of scale 7, are adapted to indicate the true temperatures of a hot body in the open.

In operation, when the radiation from a hot body falls upon the junction of athermocouple located in the total radiation pyrometer, a thermoelectric force is developed and pointer .1 swings over the scale 2, and finally comes to rest oppos'te a number or a graduation on scale 2 which indicates a certa1 n temperature, and at the same time the pointer stands opposite a graduation on scale 3 which indicates another temperature which bears a certain relation to the temperature indicated by scale 2, and which relation will now be described.

At present, all radiation pyrometers are adapted to indicate black body temperatures only, that is the temperature that is obtained by measuring the radiations which emanate from the interior .of a heated inclosure, thus, if a pyrometer is sighted upon a piece of iron surrounded by heated walls and in temperature equilibrium with the walls, the pyrometer will indicate the true or gthermo-dynamic temperature of the piece of iron, but if the-iron is removed from the inclosure and the pyrometer is again sighted upon it, it will indicate an apparent temperature which is somewhat less than the true temperature of the iron. This apparent temperature is called the black body temperature. Moreover, the black body temperature that is determined by an optical pyrometer will be different from the black body temperature that is determined by means of a total radiation pyrometer. Suppose, for example, a piece of iron has a true temperature of 1200 degrees absolute, an optical pyrometer when sighted upon the iron, the iron being in the open, would indicate a temperature of about 1125 degrees, while a total radiation pyrometer would indicate a temperature as low at v900 degrees. It is thus seen that the black body temperature is not only different from the themodynamictemperature of a hot body, but that it-is different according as it is determined by different types of pyrometers.

In illustration of this point, Fig. 3 shows a diagram representing a hollow body, which has a small opening 0. This body is heated and the total radiation pyrometer sighted through the opening 0 in a direche pyrometer will indicate on the scale 2 the black body temperature of the heated body. Since the radiation comes from the interior of the body, black body conditions obtain and the black body temperature is equal to the true temperature. If, however, the pyrometer is sighted on the outside of the body, the pyrometer scale usually employedand such as is indicated at 2 on the drawings will not give the correct temperaturevbut an apparent temperature. 1 i

The same statements apply to the indication of the temperature of an incandescent inclosure such as a furnace and to the indication of the temperature of such body when outside of the furnace.

0 Under the former circumstances, the body is said to be under black body conditions.

.My invention consists in providing means whereby the true temperature existing when the object is notunder black bodyconditions may be instantly observed from the scale, the proper calibration of which scale isbased upon certain discoveries and calculations made by me and based upon the.relation of such true-temperature to the black body temperature.

.The energy of a black body in terms of its absolute temperature may be expressed bythe Stefl'an-Boltzmann radiation law.

Referring to Fig. 8, letJ be the intensity of the radiation emanating from the interior of. the inclosure, and T the correspond ing temperature of, the interior. Also, let J represent the intensity of the radiation from the exterior and T the corresponding temperature. T is the true temperature of the body and T the corresponding black body temperature which is less than T. The Stefian-Boltzmann law may be written in the form where J :the energy of the radiation, T: the absolute temperature," and O=a constant. r

In the above equation, T represents the temperature and J the energy when the object is under black body conditions. Now let J represent the energy, and T the apparent temperature when the same is not under black body conditions; that is, in the case of a piece of iron in the furnace, T would represent thetemperature observed by the pyrometer and would be the true temperature, while T would be the temperature that the pyrometer would indicate after the body is removed from the furnace.

The temperature of the body outside the furnace will the following be determined equation J =CT 4 Combining the two equations This equation may be put in the form according to log. =4 log. 12 4 (log. T log. T)

But

log. T=log. T J,; log. A

the ratio of the energy emitted by I log. Tzlog. T +7c log. A.

t tty er ey Suppose for example that a metal has an emissive power of 0.30 and that its black body temperature T as determined by a total radiation pyrometer is 1000 degrees absolute. Its true temperature is from the above equation.

=1000 1.351)-1351 abs. In this manner the following table was where constructed Black body True temperatures. temperatures. T T 700 946 800 1081 900 1216 1000 1351 1100 1486 1200 1621 1300 1757 1400 1892 1500 2027 1600 2162 In this way the true temperature of any heated body can be determined if its emissive power is known.

The method of constructing a true temperature scale such as is indicated by the numeral 3 in the drawings, for any type of total radiation pyrometer is readily seen.

What I claim is: 1. A radiation pyrometer, having a scale indicating black body temperatures associated with a scale calibrated to indicate true temperatures of the body when not under black body conditions.

2. A total radiation pyrometer, having a scale indicating black body temperatures associated with a scale calibrated relatively to the black body scale to indicate true temperatures of the body when not under black body conditions, said scales being inscribed within arcs of circles whose center is the log. Tzlog. T +lc in which T represents the true temperature of a hot body and T the black body temperature of the hot body and in which 70 represents a constant depending upon the material of which the body is composed.

In testimony whereof I aflix my signature in presence of two witnesses.

GLENN A. SHOOK. [Ls] Witnesses:

O. A. RANDOLPH, W. H. BAIR.

Gopiea of this patent may be obtained for five cents each, by addressing the "Commissioner of Patents. Washington, D. G. 

